Circuit breakers



5, 1959 c. J. KERSLAKE 2,901,720

CIRCUIT BREAKERS Filed July 22, 1957 United States Patent CIRCUIT BREAKERS Cyril Jack Kerslake, Swindon, England, assignor to The Plessey Company Limited, Ilford, England, a British company Application July 22, 1957, Serial No. 676,698

Claims priority, application Great Britain July 20, 1956 5 Claims. (Cl. 338-163) This invention providesa novel circuit breaker for electric circuits suitable for use as a main switch for miniature electronic apparatus, particularly, as a switch combined with a volume-control device for transistoroperated hearing aids.

According to the invention the circuit breaker comprises a spring blade fixed at one point of its length to a base member so as to be urged resiliently away from contact means, and provided with a cam follower coperating with a circular cam track on a rotary control member so as to be resiliently deflected by said cam track towards said contact means and close a circuitcontrol contact when said control member is in an operative position but be allowed to move under the effect of its resilience to open said circuit when said control member is in a predetermined switch-off position.

In the accompanying drawing, an embodiment is illus trated which is an exploded sectional elevation.

This embodiment, which may be assumed to be the control unit of a hearing aid, comprises a spring in the form of a closed ring a, which has part of its peripheral length rigidly connected to a potentiometer base h 6. g. by rivets b, and is bent so that it normally extends at an angle from the base and thus is clear of two contacts 0, through which the main energising circuit for the instrument passes. A potentiometer track d, which may be used for a volume control or for other regulating purposes, is arranged to encircle concentrically the annular blade spring a, and a control-knob spindle e, which passes through the open centre of the ring a and a bore g in the base h, carries a cup-shaped control knob j, which co-operates with the base h to encase the spring a and potentiometer track d. At a point diametrically opposite to its point of attachment, the ring-shaped spring a is bent to form a hump i projecting away from the base h.

The cup-shaped knob f is provided at the inner side of its bottom j with a cam formed as an annular projection k of such height that, as long as the hump i of spring a which acts as a cam follower, rides on the projection, the spring a is forced into engagement with the contacts 0, thus maintaining the hearing aid or other device energised. The projection k is, however, interrupted by a notch 1, into which the hump i can recede, thus allowing spring a to disengage the contacts 0, when the knob f is turned beyond the minimum-volume position. The volume control or other potentiometer or resistor control may be eifected by means of a wiper m extending along the bottom of the notch 1, which co-operates with the track d and is carried by the spindle e, which serves as a terminal, the ends of the track being connected to terminal pins n.

What is claimed is:

l. A variable resistor device comprising an approximately plate-shaped insulating base equipped on one surface with a part-circular resistor track, an operating member of insulating material, means including a spindle arranged approximately co-axially with said track and connecting said operating member to said base for rotation of said operating member relative to said base about the axis of said spindle while restraining axial relative movement of said base and said operating member, a conductive wiper element secured in said operating member in contact with said spindle and extending from said spindle to a point facing said track for movement with said operating member along said track, an annular contact blade of resilient material having one point fixed to the base so as to surround the spindle substantially concentrically inside the track in insulatedrelation to the track and spindle, said blade having a cam portion projecting away from the base and arranged in approximate diametric opposition to the said point, at least one contact member fixed in the base projecting from said base towards said blade laterally of the plane containing the spindle axis and the centre of said cam portion, said contact blade being so arranged as to tend to assume a position inclined to the base plate and clear of said at least one fixed contact, an at least part-circular cam track on said control member projecting towards the base plate co-axially with the resistor track for cooperation with said cam portion to flex the contact blade into pressure contact with said at least one fixed contact, said cam track being formed with at least one recess allowing the contact blade to return resiliently to a contact breaking position when the wiper element reaches a predetermined point on the resistor track.

2. A resistor device as claimed in claim 1, wherein the wiper element extends through such recess of the cam track.

3. A resistor device as claimed in claim 2, wherein the operating member comprises a cap-like body of insulating material having a collar portion encircling the resistor track. a i 4. A resistor device as claimed in claim 2, wherein the spindle is formed with a shoulder facing the operating member, the wiper element being clamped axially between the said shoulder and operating member.

5. A resistor device as claimed in claim 1, wherein the base has a flat surface to which the contact blade is secured, and which is provided with the resistor track.

References Cited in the file of this patent UNITED STATES PATENTS 

